As for the means for connecting electronic parts to each other, connecting materials, such as an anisotropic conductive film (ACF), an anisotropic conductive paste (ACP), have been conventionally used.
The anisotropic conductive film is a film-shaped connecting material, which is formed, for example, by dispersing conductive particles in an insulating binder containing a thermoset resin. The binder containing the thermoset resin is thermally cured by thermocompression bonding the parts of electrodes of the electronic parts, which are to be anisotropic conductively connected together, via the ACF, to thereby connect the electronic parts.
For example, the anisotropic conductive paste contains an insulating binder, conductive particles, and a solvent (see, for example, PTL 1 and PTL 2). A method for using the ACP containing the solvent is, for example, as follows. As the ACP is printed on an electronic part, such as a flexible printed circuit (FPC), and heated to dry, a coating film formed of the ACP is formed on an area of an electrode of the electronic part. The FPC, to which the coating film formed of the ACP has been formed, is often transported in this state at room temperature. As for the ACP, therefore, also used is a type thereof where a non-reactable binder that is not cured by heat is used.
As for connection between electronic parts, recently required has been connection at low temperature and low pressure within a short period. Connection at low temperature is desired because a thermal damage to electronic parts is reduced, variation in heating temperature (heating temperature at an area of an electrode changes whether or not a part, which is provided at a position extended from a wire, is linked with the wire connected to the area of the electrode, which causes variation in temperature, and the variation becomes particularly significant as a packaging density increases) at the time of connection is prevented, and load to packaging equipment is reduced. Connection at low pressure is desired because damage applied to a thin substrate or a touch panel is reduced. Connection with a short period is desired in view of productivity.
However, the conventional anisotropic conductive film uses a thermoset resin, and hence curing is cause during storage, as the anisotropic conductive film is designed to correspond to connection at low temperature within a short period. Therefore, it is necessary to make a storage period short, and such anisotropic conductive film is not suitable for practical use.
Moreover, the conventional anisotropic conductive paste needs to reduce a viscosity of the ACP for use, when it is designed to correspond to connection at low pressure. When the viscosity of the ACP is reduced, the binder in the ACP can not bear the restoring force of the electronic parts caused just after the termination of the thermal pressure bonding. As a result, the deformation of the conductive particles cannot be maintained, which causes insufficient connection resistance.
Accordingly, it is currently desired to provide an anisotropic conductive film, which can realize connection at low temperature and low pressure within a short period while maintaining sufficient connection resistance, as well as a connecting method using the anisotropic conductive film, and a bonded structure using the anisotropic conductive film.